LONDON — London police said Friday that a deadly fire last week that killed at least 79 people was started by a fridge freezer — the first official confirmation on the cause of the blaze.

The fridge freezer — a Hotpoint FF175BP — was not subject to a product recall, police said, adding that one of the key concerns in their investigation is how a fire that began in the kitchen of one apartment spread so rapidly though a 24-story high-rise.

The police also said that insulation and tiles used in the building’s exterior cladding have failed fire safety tests.

“Preliminary tests on the insulation samples collected from Grenfell Tower showed that they combusted soon after the test started. The initial test on the cladding tiles also failed the safety tests,” Detective Superintendent Fiona McCormack told reporters.

Hotpoint issued a “product notice” for the appliance identified by authorities as the source of the blaze. The company asked owners to check their models and serial numbers and complete an online form.

“We have been made aware of a possible incident involving a Hotpoint branded Fridge Freezer, manufactured between March 2006 and July 2009, model numbers FF175BP (white) and FF175BG (graphite),” the notice said.

There has been widespread attention on the building’s exterior cladding. Combustible cladding has been blamed for rapid fires at high-rise buildings in places such as Dubai and Melbourne, Australia.

The British government is testing hundreds of high-rise apartments to see if they have exterior tiles that are potentially flammable. So far, 11 buildings have been found to have cladding similar to that used on Grenfell Tower.

McCormack said that the police were considering manslaughter charges among the possible offenses in relation to the fire.

“We are looking at every criminal offense, from manslaughter. We are looking at every health and safety and fire safety offenses, and we are reviewing every company at the moment involved in the building and refurbishment of Grenfell Tower,” she said.

Officials are concerned that they don’t have the full picture of who, exactly, was in the tower on the night of the blaze. They have stressed that any people involved in the fire, or who have information about victims, will not have their immigration status checked amid concerns that some of those in the building may have been staying there illegally.

Many locals say they do not believe the official death toll. On the streets around Grenfell Tower — now a blackened hulk of a building — missing-person photos are attached to railings, buildings and bus stops. One girl, Amaya Ahmedin, who turned 3 in February, is pictured in a golden party hat next to her smiling parents.

On one of the many walls of condolences near the tower, one local wrote that they believed, based on “community with info from police and ambulance,” there were 160 dead.

Police say that 79 people are dead or presumed dead, but they suggested that the death toll could rise.

“I fear that there are more. I do not know who they are at the moment,” McCormack said as she appealed for those with information to come forward.